The lower esophageal sphincter (LES) is prone to relaxing intermittently. As a consequence, fluid from the stomach can pass into the esophagus since the mechanical barrier is temporarily lost at such times, an event hereinafter referred to as “reflux”.
Gastroesophageal reflux disease (GERD) is the most prevalent upper gastrointestinal tract disease. Current pharmacotherapy aims at reducing gastric acid secretion, or at neutralizing acid in the esophagus. The major mechanism behind reflux has been considered to depend on a hypotonic lower esophageal sphincter. However, recent research (e.g. Holloway & Dent (1990) Gastroenterol. Clin. N. Amer. 19, pp. 517-535) has shown that most reflux episodes occur during transient lower esophageal sphincter relaxations (TLESR), i.e. relaxations not triggered by swallows. It has also been shown that gastric acid secretion usually is normal in patients with GERD.
Consequently, there is a need for a therapy that reduces the incidence of TLESR and thereby prevents reflux.
GABAB-receptor agonists have been shown to inhibit TLESR, which is disclosed in WO 98/11885 A1.
GABAB Receptor Agonists
GABA (4-aminobutanoic acid) is an endogerous neurotransmitter in the central and peripheral nervous systems. Receptors for GABA have traditionally been divided into GABAA and GABAB receptor subtypes. GABAB receptors belong to the superfamily of G-protein coupled receptors (GPCRs).
The most studied GABAB receptor agonist baclofen (4-amino-3-(p-chlorophenyl)butanoic acid; disclosed in CH 449046) is useful as an antispastic agent. EP 356128 A2 describes the use of the GABAB receptor agonist (3-aminopropyl)methylphosphinic acid for use in therapy, in particular in the treatment of central nervous system disorders.
EP 463969 A1 and FR 2722192 A1 disclose 4-aminobutanoic acid derivatives having different heterocyclic substituents at the 3-carbon of the butyl chain. EP 181833 A1 discloses substituted 3-aminopropylphosphinic acids having high affinities towards GABAB receptor sites. EP 399949 A1 discloses derivatives of (3-aminopropyl)methylphosphinic acid, which are described as potent GABAB receptor agonists. Still other (3-aminopropyl)methylphosphinic acids and (3-aminopropyl)phosphinic acids have been disclosed in WO 01/41743 A1 and WO 01/42252 A1, respectively. Structure-activity relationships of several phosphinic acid analogues with respect to their affinities to the GABAB receptor are discussed in J. Med. Chem. (1995), 38, 3297-3312. Sulphinic acid analogues and their GABAB receptor activities are described in Bioorg. & Med. Chem. Lett. (1998), 8, 3059-3064. For a more general review on GABAB ligands, see Curr. Med. Chem.-Central Nervous System Agents (2001), 1, 27-42.
Positive Allosteric Modulation of GABAB Receptors
2,6-Di-tert-butyl-4-(3-hydroxy-2,2-dimethylpropyl)phenol (CGP7930) and 3-(3,5-di-tert-butyl-4-hydroxyphenyl)-2,2-dimethylpropanal (disclosed in U.S. Pat. No. 5,304,685) have been described to exert positive allosteric modulation of native and recombinant GABAB receptor activity (Society for Neuroscience, 30th Annual Meeting, New Orleans, La., Nov. 4-9, 2000: Positive Allosteric Modulation of Native and Recombinant GABAB Receptor Activity, S. Urwyler et al.; Molecular Pharmacol. (2001), 60, 963-971).
N,N-Dicyclopentyl-2-methylsulfanyl-5-nitro-pyrimidine-4,6-diamine has been described to exert positive allosteric modulation of the GABAB receptor (The Journal of Pharmacology and Experimental Therapeutics, 307 (2003), 322-330).
For a recent review on allosteric modulation of GPCRs, see: Expert Opin. Ther. Patents (2001), 11, 1889-1904.